The government is a monopol trader, he buys the product from the producer , then sell to consummer, his income is a function of tax rate and the total quantity of the goods.
T(t, q)=t.q, t:tax rate, q: quantity.
Here it is very similar as the monopolist theory, the target of govrnment is also to maximize the total income: T.
Do the first order derivate, then you can understand the laffer-curve , it means there is a optimum point of tax rate, links of this point, the government can raise t to get more income, the right of this point , government should reduce t, to let q bigger, also get a bigger income.
Problem is that , people do not know which point is actual situation, ahould we reduce t, or should we raise t? There´are till know also no consistent solution, only discussion on the paper, less empirical evidence.